Rivers Flashcards
Is the hydrological cycle an open system and why
No, because new water is never added to the earth or its atmosphere, nor is water ever removed
How does the water cycle work
- Energy from the Sun heats the surface of the Earth
- Water is evaporated from oceans, rivers, lakes, etc
- The warm, moist air rises because it is less dense
- Condensation occurs when water vapour is turned back into water droplets as it cools down
- Precipitation occurs as water droplets get bigger and heavier they begin to fall as rain, snow and sleet, etc
What are the processes in the water cycle
Evaporation
Condensation
Precipitation
Surface run off
Percolation/Infiltration
Groundwater flow
Transpiration
What is a drainage basin
Area of land where precipitation collects and drains into any body of water
What are the parts of a drainage basin
Mouth
Source
Watershed
Main river channel
Tributary
Confluence
Is a drainage basin part of an open system and why
Yes, water that enters as input from precipitation flows out of the system as output of water into the sea and evaporation of water into the atmosphere
What are River processes and what do they do
Shape the land in many ways as the river moves from its source to its mouth. Erosion, transportation and deposition contribute to this
What is River discharge
Total volume of water flowing through at any given point and is measured in cubic metres per second
What are 3 factors affecting work carried out by a river
- Velocity/energy
- Volume
- Bedrock
What are 4 main types of river erosion and explain them
Hydraulic action- Force of the river against the banks can cause air to be trapped in cracks and crevices. Pressure then weakens the banks and gradually wears it away
Abrasion- Rocks carried along by the river wear down the river bed and banks
Attrition - rocks being carried by the river knock each other and break into smaller, smoother and rounder particles
Solution - soluble particles are dissolved into the river
What are 4 river transport processes
Solution- Minerals are dissolved in the water & carried in solution
Suspension- Fine light material is carried along in the water
Saltation- Small pebbles & stones are bounced along the river bed
Traction- Large boulders and rocks are rolled along the river bed
What is deposition, where can it happen, and what can deposition at the mouth of the river create
When a river loses energy, it will drop or deposit some of the material it is carrying
Deposition may take place when a river enters an area of shallow water or when the volume of water decreases- for example, after a flood or during times of drought
Deposition is common towards the mouth
Deposition at the mouth of a river can form deltas, eg: the Mississippi Delta
Characteristics and processes in upper valley
Vertical erosion with hydraulic action, abrasion and attrition as dominant processes
Traction and saltation at high flow
Load size is large and angular
V shaped valleys
Characteristics and processes in middle reaches
Channel is deeper and wider
Vertical erosion decreasing in importance, more lateral erosion and deposition
Suspension is the main transportation type
Load becomes smaller and less angular
Characteristics and processes in lower reaches
Channel is at its deepest and widest, may be tidal
More deposition than erosion
Fine material deposited
Large amount of load but the size is very small and very rounded
How are V-shaped valleys and Interlocking spurs formed
In upper course, river is fast flowing but there is little water and load. The river/stream does not have erosive power to remove the hillsides so it makes its way around hills forming Interlocking spurs.
The stream erodes downwards and forms V-Shaped valleys
How are waterfalls and gorges formed
Water flows where hard rock lies over soft rock
Water erodes soft rock more easily undercutting the hard rock
Overhang is formed
Overhang collapses eventually
Plungepool develops
Waterfall retreats upstream
Steep gorge like valleys are formed
How are potholes formed
Boulders broken off by erosion that sit on the river bed create swirling current
How is a meanders formed
In middle course, river has more energy and a high volume of water.
river erodes laterally, to right side and then to the left side, it forms large bends, and then horseshoe-like loops called meanders
Formation of meanders is due to deposition and erosion
FOrce of water erodes and undercuts the river bank on the outside of the bend where water flow has the most energy due to decreased friction
On the inside of the bend, river flow is slower, material is deposited as there is more friction
How is an oxbow lake formed
The gap between the arms of the rivers narrowed by erosion
river breaks through narrow gap when high rainfall and flooding occurs
Current along straighter path becomes dominant
Old path of river now dry and an oxbow lake remains
How is a floodplain formed
- Area of alluvial deposits
- Valley is eroded to create a wide valley floor
- Deposits layers of alluvial material on the slip off slopes building up into a large flood plain
How is a Levee formed
During flood the thickest and coarsest sediments deposited at channel edges
Thin and fine sediments deposited over outer parts of floodplain
natural levees built up after many floods
How is a delta formed
When river meets the sea its velocity suddenly reduces
Reduction in velocity means the the rivers load is deposited at the mouth of the river
If the river deposits quicker than the sea can erode then a delta starts to develop
What is lag time
The delay between peak rainfall and peak discharge
What is shown on a storm hydrograph and how can that change
The discharge of a river is shown on a graph called a flood or storm hydrograph. It shows the rainfall amount and then the discharge of the river. Most of the rain falls onto the land rather than directly into the river. The water then will make its way into the river and you can use a hydrograph to see how quickly this occurs.
Different catchment areas will have different flood hydrographs. Some, with steep slopes and little vegetation, will rise very quickly, and can be described as a “flashy river”.
What are some factors that affect river regime
Vegetation and land use
Rainfall
Climate
Shape of land, gradient of slope
Soil type and depth
Type of bedrock
Size and shape of river basin
